• They became an attractive target for 'entryism' and as soon as the negotiations were over, a large section of their party left to join a different party - the party for whom they had clearly been the agents for some considerable time

Indeed, one of national anarchists 'principal tactics is called "entryism," defined in one of the movement's how-to guides as "the name given to the process of entering or infiltrating bona fide organizations, institutions and political parties with the intention of gaining control of them for our own ends."

The major political issue here [for voters] will be to say stop to the dominance and hegemony of the monarchy in the political system; to say that after more than fifteen years of “democratic transition”, a term so cherished by the communicators and spin doctors of the Kingdom - and while we expected a shift to a parliamentary monarchy - the entryism of the king's friend is a giant leap backward.

On a side note, there have been reports of entryism from both Labour and the Tories; Jim Fitzpatrick reckons Labour are being taken over by islamists, whilst there is concern that the conservatives are being unduly influenced by evangelical christians.

Wikipedia has some examples of entryism more generally, although most are not by groups hostile to the original group, but rather by groups on the fringe of the original group, hoping to hijack it in their preferred direction the canonical example being Trotskyists trying to take over democratic-socialist parties.

Since then Darren Johnson as the Chair of the London Assembly has provided written support for my FOOTBALL AGAINST RACISM IN EUROPE FARE case for the defence against neo-Nazi entryism into London's Sporting/Planning Arena 1991-2009, and Doreen Lawrence has also asked me to "keep up the good work".